Here's how question 6 is worded on form IMM5669E (Schedule A Background Declaration):
Have you ever:
b) been convicted of, or are you currently charged with,
on trial for, or party to a crime or offence, or subject
of any criminal proceedings in any other country?
Followed by:
j) been detained, incarcerated or put in jail?
Now, arguably you could probably answer no to 6b (if you were never convicted of the DUI), but...you would certainly need to answer yes to 6j unless you were NOT arrested, detained or put in jail for the DUI.
It's a tough call.